Neurological damage in patients irradiated twice on the spinal cord: a morphologic and electrophysiological study

Comparative Evaluation of Proton Therapy and Volumetric Modulated Arc Therapy for Brachial Plexus Sparing in the Comprehensive Reirradiation of High-Risk Recurrent Breast Cancer

Purpose

Recurrent or new primary breast cancer requiring comprehensive regional nodal irradiation after prior radiation therapy (RT) to the supraclavicular area and upper axilla is challenging due to cumulative brachial plexus (BP) dose tolerance. We assessed BP dose sparing achieved with pencil beam scanning proton therapy (PBS-PT) and photon volumetric modulated arc therapy (VMAT).

Methods and Materials

In an institutional review board-approved planning study, all patients with ipsilateral recurrent breast cancer treated with PBS-PT re-RT (PBT1) with at least partial BP overlap from prior photon RT were identified. Comparative VMAT plans (XRT1) using matched BP dose constraints were developed. A second pair of proton (PBT2) and VMAT (XRT2) plans using standardized target volumes were created, applying uniform prescription dose of 50.4 per 1.8 Gy and a maximum BP constraint <25 Gy. Incidence of brachial plexopathy was also assessed.

Results

Ten consecutive patients were identified. Median time between RT courses was 48 months (15-276). Median first, second, and cumulative RT doses were 50.4 Gy (range, 42.6-60.0), 50.4 Gy relative biologic effectiveness (RBE) (45.0-64.4), and 102.4 Gy (RBE) (95.0-120.0), respectively. Median follow-up was 15 months (5-33) and 18 months for living patients (11-33) Mean BP max was 37.5 Gy (RBE) for PBT1 and 36.9 Gy for XRT1. Target volume coverage of V85% (volume receiving 85% of prescription dose), V90%, and V95% were numerically lower for XRT1 versus PBT1. Similarly, axilla I-III and supraclavicular area coverage were significantly higher for PBT2 than XRT2 at dose levels of V55%, V65%, V75%, V85%, and V95%. Only axilla I V55% did not reach significance (P = .06) favoring PBS-PT. Two patients with high cumulative BPmax (95.2 Gy [RBE], 101.6 Gy [RBE]) developed brachial plexopathy symptoms with ulnar nerve distribution neuropathy without pain or weakness (1 of 2 had symptom resolution after 6 months without intervention).

Conclusions

PBS-PT improved BP sparing and target volume coverage versus VMAT. For patients requiring comprehensive re-RT for high-risk, nonmetastatic breast cancer recurrence with BP overlap and reasonable expectation for prolonged life expectancy, PBT may be the preferred treatment modality.

Proposal of human spinal cord reirradiation dose based on collection of data from 40 patients

PURPOSE

Driven by numerous reports on recovery of occult radiation injury, reirradiation of the spinal cord today is considered a realistic option. In rodents, long-term recovery was observed to start at approximately 8 weeks. However, prospective clinical studies are lacking. Therefore, a combined analysis of all published clinical data might provide a valuable basis for future trials.

METHODS AND MATERIALS

We collected data from 40 individual patients published in eight different reports after a comprehensive MEDLINE search. These represent all patients with data available for dose per fraction and total dose of each of both treatment courses. We recalculated the biologically effective dose (BED) according to the linear-quadratic model using an alpha/beta value of 2 Gy for the cervical and thoracic cord and 4 Gy for the lumbar cord. In this model, a dose of 50 Gy given in single daily fractions of 2 Gy is equivalent to a BED of 100 Gy(2) or 75 Gy(4). For treatment with two daily fractions, a correction term was introduced to take incomplete repair of sublethal damage into account.

RESULTS

The cumulative doses ranged from 108 to 205 Gy(2) (median dose, 135 Gy(2)). The median interval between both series was 20 months. Three patients were treated to the lumbar segments only. The median follow-up was 17 months for patients without myelopathy. Eleven patients developed myelopathy after 4-25 months (median, 11 months). Myelopathy was seen only in patients who had received one course to a dose of > or =102 Gy(2) (n = 9) or were retreated after 2 months (n = 2). In the absence of these two risk factors, no myelopathy developed in 19 patients treated with < or =135.5 Gy(2) or 7 patients treated with 136-150 Gy(2). A risk score based on the cumulative BED, the greatest BED for all treatment series in a particular individual, and interval was developed. Low-risk patients remained free of myelopathy and 33% of intermediate-risk patients and 90% of high-risk patients developed myelopathy.

CONCLUSION

On the basis of these literature data (and with due caution), the risk of myelopathy appears small after < or =135.5 Gy(2) when the interval is not shorter than 6 months and the dose of each course is < or =98 Gy(2). We would recommend limiting the dose to this level, whenever technically feasible. However, it appears prudent to propose the collection of prospective data from a greater number of patients receiving doses in the range of 136-150 Gy(2) to assess the safety of higher retreatment doses for those patients in whom limited doses might compromise tumor control.

Retreatment of the spinal cord with palliative radiotherapy

PURPOSE

We conducted this retrospective review of patients whose spinal cord was irradiated twice to evaluate the outcome in terms of palliation and long-term side effects.

METHODS AND MATERIALS

Eight patients (4 females, 4 males; median age: 67 years) were identified whose spinal cord had been irradiated twice between July 1990 and July 1997, usually for the management of bone metastases. All patients were followed up until their death from progressive disease. The Karnofsky performance score at the time of retreatment ranged from 20% to 90%. Total dose for the first treatment ranged from 29 to 50 Gy (median: 38 Gy) with single doses 1.25-3 Gy; the total dose for the retreatment ranged from 29 to 38 Gy (median: 30 Gy) with a single dose 1.8-4 Gy. The cumulative dose ranged from 59 to 88 Gy (median: 67.5 Gy). The overlap in the site of retreatment consisted of 1-3 segments, whereas in one patient, 2 single segments were treated twice. The outcome in terms of progressive disease, the palliative effects, and the development of myelopathy was assessed retrospectively.

RESULTS

The median interval to reirradiation was 30 months (range: 6-63 months), and the median follow-up after the last treatment was 16 months (range: 5-44 months). After reirradiation, 4/7 patients experienced complete pain relief, 2/7 patients experienced minor pain relief, and only 1 patient showed no change. Two patients with paraparesis experienced complete recovery. All patients tolerated retreatment very well. No serious acute side effects requiring any therapy were seen. During follow-up, no patient showed treatment-induced neurologic abnormalities affecting motor and sensory function, and all patients were able to walk and were continent for stool and urine.

CONCLUSION

On the basis of the findings in this limited number of patients, it is not possible to give clear and general recommendations concerning the optimal total dose and fraction size that will have maximal palliative effects and minimal side effects. However, for the purpose of palliation, retreatment within the dose range used at our institution should be considered, taking the patient's expected life span and clinical symptoms into account.

Radiation-induced myelopathy in long-term surviving metastatic spinal cord compression patients after hypofractionated radiotherapy: a clinical and magnetic resonance imaging analysis

BACKGROUND AND PURPOSE

Hypofractionated radiotherapy is often administered in metastatic spinal cord compression (MSCC), but no studies have been published on the incidence of radiation-induced myelopathy (RIM) in long-term surviving patients. Our report addresses this topic.

PATIENTS AND METHODS

Of 465 consecutive MSCC patients submitted to radiotherapy between 1988 and 1997, 13 live patients (seven females, six males, median age 69 years, median follow-up 69 months) surviving for 2 years or more were retrospectively reviewed to evaluate RIM. All patients underwent radiotherapy. Eight patients underwent a short-course regimen of 8 Gy, with 7 days rest, and then another 8 Gy. Five patients underwent a split-course regimen of 5 Gy x 3, 4 days rest, and then 3 Gy x 5. Only one patient also underwent laminectomy. Full neurological examination and magnetic resonance imaging (MRI) were performed.

RESULTS

Of 12 patients submitted to radiotherapy alone, 11 were ambulant (eight without support and three with support) with good bladder function. In nine of these 11 patients, MRI was negative; in one case MRI evidenced an in-field relapse 30 months after the end of radiotherapy, and in the other, two new MSCC foci outside the irradiated spine. In the remaining patient RIM was suspected at 18 months after radiotherapy when the patient became paraplegic and cystoplegic, and magnetic resonance images evidenced an ischemic injury in the irradiated area. The only patient treated with surgery plus postoperative radiotherapy worsened and remained paraparetic. Magnetic resonance images showed cord atrophy at the surgical level, explained as an ischemic necrosis due to surgery injury.

CONCLUSIONS

On the grounds of our data regarding RIM in long-term surviving MSCC patients, we believe that a hypofractionated radiotherapy regimen can be used for the majority of patients. For a minority of patients, more protracted radiation regimens could be considered.

Extent and kinetics of recovery of occult spinal cord injury

PURPOSE

To obtain clinically useful quantitative data on the extent and kinetics of recovery of occult radiation injury in primate spinal cord, after a commonly administered elective radiation dose of 44 Gy, given in about 2 Gy per fraction.

METHODS AND MATERIALS

A group of 56 rhesus monkeys was assigned to receive two radiation courses to the cervical and upper thoracic spinal cord, given in 2.2 Gy per fraction. The dose of the initial course was 44 Gy in all monkeys. Reirradiation dose was 57.2 Gy, given after 1-year (n = 16) or 2-year (n = 20) intervals, or 66 Gy, given after 2-year (n = 4) or 3-year (n = 14) intervals. Two animals developed intramedullary tumors before reirradiation and, therefore, did not receive a second course. The study endpoint was myeloparesis, manifesting predominantly as lower extremity weakness and decrease in balance, occurring within 2.5 years after reirradiation, complemented by histologic examination of the spinal cord. The data obtained were analyzed along with data from a previous study addressing single-course tolerance, and data from a preliminary study of reirradiation tolerance.

RESULTS

Only 4 of 45 monkeys completing the required observation period (2-2.5 years after reirradiation, 3-5.5 years total) developed myeloparesis. The data revealed a substantial recovery of occult injury induced by 44 Gy within the first year, and suggested additional recovery between 1 and 3 years. Fitting the data with a model, assuming that all (single course and reirradiation) dose-response curves were parallel, yielded recovery estimates of 33.6 Gy (76%), 37.6 Gy (85%), and 44.6 Gy (101%) of the initial dose, after 1, 2, and 3 years, respectively, at the 5% incidence (D(5)) level. The most conservative estimate, using a model in which it was assumed that there was no recovery between 1 and 3 years following initial irradiation and that the combined reirradiation curve was not necessarily parallel to the single-course curve, still showed an overall recovery equivalent to 26.8 Gy (61%). The spinal cords of symptomatic monkeys consistently revealed a mixture of white matter necrosis and vascular injury, but the majority of spinal cords of asymptomatic animals did not exhibit overt lesions detectable by light microscopy.

CONCLUSION

Combined analysis with the data of the previous studies yielded firm evidence that the spinal cord has a large capacity to recover from occult radiation injury induced by a commonly prescribed elective dose. This finding strengthens the rationale for selective use of radiotherapy to treat second primary tumors arising in previously irradiated tissues or late recurrences. However, some caution should be exercised in applying quantitative experimental data, because the length of follow-up in these experiments was limited to 2-2.5 years after reirradiation, whereas human myelopathy cases occasionally occur after longer latency. Because there is a large variation in long-term recovery among tissues, the tolerance of other tissues at risk should also be taken into account in prescribing therapy.

Tissue tolerance to reirradiation

There are increasing requests for delivering a second course of radiation to patients who develop second primary tumors within or close to previous radiotherapy portal or late in-field recurrences. Rational treatment decisions demand rather precise knowledge on long-term recovery of occult radiation injury in various organs. This article summarizes available experimental and clinical data on the effects of reirradiation to the skin, mucosa, gut, lung, spinal cord, brain, heart, bladder, and kidney. The data reveal that, in general, acutely responding tissues recover radiation injury within a few months and, therefore, can tolerate another full course of radiation. For late toxicity endpoints, however, tissues vary considerably in their capacity to recover from occult radiation damage. The heart, bladder, and kidney do not exhibit long-term recovery at all. In contrast, the skin, mucosa, lung, and spinal cord do recover subclinical injury partially to a magnitude dependent on the organ type, size of the initial dose, and, to a lesser extent, the interval between radiation courses. The available clinical data have inspired many radiation oncologists to undertake systematic studies addressing the efficacy and toxicity of reirradiation in various clinical settings. Hopefully, systematic scoring, collection, and analysis of patient outcome will produce quantitative data useful for clinical practice.

Outcome after spinal reirradiation for malignant epidural spinal cord compression

Radiotherapy is effective for most cases of spinal cord compression. Although recurrent spinal cord compression is a common problem, little is known about whether reirradiation preserves neurologic function and what risk of radiation myelopathy it carries. To investigate this question, we reviewed patients at the Mayo Clinic between 1975 and 1992 undergoing two or more courses of radiotherapy to the same segment of the spinal column with radiographically documented epidural disease at the time of reirradiation to determine outcome as measured by the ability to walk and by survival. Fifty-four patients met the study criteria. Radiation doses for the first course ranged from 2,250 to 5,400 cGy (median, 3,000 cGy), and total dose for all courses to the reirradiated spinal segment ranged from 3,650 to 8,089 cGy (median, 5,425 cGy). All patients were ambulatory following the first course of radiation, 40 (74%) were ambulatory at the onset of reirradiation, and 42 (78%) were ambulatory at the end of reirradiation. Thirty-seven patients (69%) remained ambulatory at their last follow-up 6 days to 80 months following reirradiation (median, 4.7 months). Five patients eventually became nonambulatory 6.5 to 35 months following reirradiation. Median survival for all patients following reirradiation was 4.2 months. We conclude that for cancer patients with progressive epidural disease following radiotherapy, reirradiation frequently preserves ambulation and carries minimal risk of radiation myelopathy during the patients' lifetime.